I. Field of the Invention
This invention relates to the generation of high intensity X-rays for use in high speed computed tomography scanners.
II. Description of Prior Art
Computed tomography scanners are known which employ conventional X-ray tubes or radioactive nuclei to provide a single source of high intensity X-rays. This single source of X-rays is mechanically revolved about an object under observation, typically through use of a revolving ring mounted in a scanner gantry. Such prior art scanners have an inherent limitation in the speed with which a particular image may be produced due to speed limitations of the mechanical revolution of the single source of x-rays.
Computed tomography scanners are also known which employ a continuous annular anode x-ray source which surrounds an object. The anode x-ray source is scanned by an electron beam to selectively produce x-rays. The electron beam is derived from a single fixed electron beam generator located along the axis of an object and is deflected to the anode by deflection coils or the like. Accordingly, a large evacuated chamber is required to enclose the electron beam generator, the annular anode, and the path of travel of the electron beam between the beam generator and the anode. Moreover, because of the necessity of manipulating an electron beam over distances of several meters, focal spot sizes of the resultant beam on the cathode are larger than desirable. This in turn limits the spacial resolution achievable in such a scanner. Accordingly, such known annular anode scanners have the disadvantages of large focal spot sizes and the requirement of large evacuated vessels with the need for active electrical devices for focusing and deflection.
Computed tomography scanners are also known to be planned which propose the use of flash X-ray sources using high voltage discharges. The utilization of sequentially pulsed, high voltage discharge sources may prove capable of high speed resolution. However, independent control of X-ray energy intensity may prove difficult to implement.
It is, accordingly, an object of the present invention to provide a computed tomography scanner in which a focal spot of desired size can be readily attained and varied easily and continuously.
It is a further object of the present invention to provide a computed tomography scanner with simplified annular X-ray tube construction.
More specifically, it is an object of the present invention to provide a computed tomography scanner employing a continuous annular anode with a reduced evacuated vessel size over known continuous annular anode computed tomography scanners.
Additional objects and advantages of the subject invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention.